Conventional lasers with annular discharge, hybrid resonators, and distributed inductances and conventional diffusion cooled lasers typically use insulating materials between the “live” electrode and ground, and not just in the radio frequency (RF) feed-through. Examples of such lasers include commercially available lasers from TRUMPF (Farmington, Conn.) including TruCoax V3, V4, and V5 production lasers.
FIG. 1A (side-on, cross-sectional view) shows the assembly of an RF excited gas laser that includes a pair of concentric electrodes 1 and 2 that form a discharge gap 11 between them and are electrically insulated and mechanically held at both ends by dielectric parts. The mirrors for the optical resonator are located at the ends of the discharge facing each other. These mirrors are an axicon 7 at one end, which is a retro-reflector, and a helix 8 at the other end, which includes in a single substrate both front and back mirrors of a typical resonator. A laser output window 12 is located on the helix carrier. The electrode assembly includes support blocks at each end to which the resonator mirrors are mounted. Each mirror is mounted on a carrier that serves as a lid for each end of the assembly.
When the outer electrode 1, inner electrode 2, and lids are assembled they form a vacuum tight chamber that holds the laser gas mixture. The inner electrode 2 is held in place by a metal bridge 3 and ceramic inserts 5 and 6. The ceramic inserts electrically insulate the inner electrode from the outer electrode. The ceramic insert 5 at the helix end is shaped like a hollow cylinder that connects the inner electrode 2 and the carrier for the helix. The helix substrate as well as the carrier has a circular opening in the center that gives access through the hollow ceramic insert 5 to the inner electrode 2 at atmospheric pressure. Through this aperture the RF feed-through assembly 9 is connected to the exposed region of the inner electrode 2 to supply RF power and for the supply and return of the cooling fluids for the inner electrode 2. The helix-end ceramic insert 5 keeps the inner electrode 2 insulated from the grounded outer electrode 1. At the axicon 7 end, the inner electrode 2 is electrically connected by an adjustable termination inductor 4 to ground.
When RF power is supplied to the inner electrode 2 through the RF feed-through 9 and a discharge is generated in the gap 11, the electrodes in combination with the generated discharge behave like a lossy transmission line for the RF power. A voltage variation occurs along the length of the electrodes as the RF power propagates in the lossy transmission line. The transmission line is terminated at the axicon 7 end by the internal adjustable termination 4. To further reduce the voltage variations and obtain a uniform discharge, distributed inductors 100 are connected between the outer electrode 1 and the inner electrode 2 at several locations outside the vacuum and along the length of the electrodes with the use of specially designed assemblies.
FIG. 1B shows an example of the coil assembly of this laser as shown and described in U.S. Pat. No. 7,778,303. As shown in FIG. 1B, inductor assembly 100 includes a conductive rod or feed-through 170 that extends through a vacuum-sealed opening 175 of outer electrode 110 and into inter-electrode gap 115. The feed-through 170 terminates at one end at a flexible conductive contact 187 that contacts an outer surface of inner electrode 105 within the vacuum. Inductor assembly 100 also includes a lead 180 that is detachably connected to the feed-through 170 using, for example, a screw 185. Inductor assembly 100 is electrically connected to outer electrode 110 by lead 180 when lead 180 makes suitable electrical contact with the outer surface of the outer electrode 110. By removing screws 185 and 186, the position of lead 180 relative to the outer surface of outer electrode 110 can be adjusted and therefore the current length from feed-through 170 to outer electrode 110 can be adjusted to adjust the value of the inductance that is produced by inductor assembly 100. Therefore, the inductance of inductor assembly 100 can be easily adjusted without having to open the vacuum seal or remove feed-through 170.